Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A display device is disclosed. The display device includes: a pixel array
portion and a driver portion for driving the pixel array portion. The
pixel array portion has rows of scanning lines, columns of signal lines,
pixels arranged in rows and columns at intersections of the scanning
lines and the signal lines, and power lines disposed in a corresponding
manner to the rows of the pixels. The driver portion includes a main
scanner, a power-supply scanner, and a signal selector. Each of the
pixels includes light-emitting devices, a sampling transistor, a driving
transistor, a retaining capacitor.

Claims:

1. A display device comprising: rows of scanning lines; columns of signal
lines; pixels arranged in rows and columns; and power lines, wherein each
of the pixels includes a light-emitting device, a sampling transistor
providing a reference potential and a signal potential from one of the
signal lines, a driving transistor, a retaining capacitor, the driving
transistor is connected between a power line and the light-emitting
device, wherein a control signal is output to the sampling transistor
while the signal line is at the reference potential, to correct a
threshold voltage for the driving transistor, and wherein the control
signal has a pulse width shorter than a time interval in which the signal
line is at the signal potential.

2. An electronic device equipped with a display device as set forth in
claim 1.

Description:

CROSS REFERENCES TO RELATED APPLICATION

[0001] This is a Continuation Application of the patent application Ser.
No. 11/878,671, filed Jul. 26, 2007, which claims priority from Japanese
Patent Application JP2006-209326 filed in the Japanese Patent Office on
Aug. 1, 2006, the entire contents of which are incorporated herein by
reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an active matrix display device
using light-emitting devices at pixels and also to a method of driving
the display device. Furthermore, the invention relates to an electronic
device incorporating such a display device.

[0004] 2. Description of the Related Art

[0005] In recent years, self-luminous flat panel displays using organic
electroluminescent devices (OEDs) as light-emitting devices have been
developed vigorously. An OED is a device making use of the phenomenon
that electroluminescence occurs when an electric field is applied to an
organic thin film. Since OEDs are driven when a voltage of less than 10 V
is applied, the devices are low power consumption devices. Furthermore,
because OEDs are self-luminous devices, no illumination may be required.
Consequently, it is easy to fabricate them with reduced weight and
thickness. In addition, the response speeds of OEDs are very fast, on the
order of microseconds. Hence, when motion pictures are displayed, there
is no afterimage.

[0007] However, in related-art active-matrix self-luminous flat panel
displays, transistors for driving the light-emitting devices are not
uniform in threshold voltage and mobility due to process variations.
Furthermore, the characteristics of the organic electroluminescent
devices vary with time. These variations in the characteristics of the
driving transistors and variations in the characteristics of the OEDs
affect the output brightness. In order to make uniform the output
brightness over the whole screen of the display device, it may be
necessary to correct the variations in the characteristics of the
transistor and OED within each pixel circuit. A display device having a
function of making such a correction at each pixel has been heretofore
proposed. However, the pixel circuit having the known correcting function
as described above would need lines for supplying corrective potentials,
switching transistors, and switching pulses. That is, the pixel circuit
is complex in configuration. An improvement of the resolution of the
display device is hindered by the fact that the pixel circuit is made up
of a large number of components.

[0008] In view of the foregoing technical issues with the related art, it
is desirable to provide a display device using a simplified pixel circuit
thereby to permit a higher resolution. It is also desirable to provide a
method of driving this display device. Especially, it is desirable to
provide a display device and a driving method capable of reliably
correcting variations among threshold voltages for driving transistors.

[0009] A display device according to one embodiment of the present
invention is fundamentally composed of a pixel array portion and a driver
portion for driving the pixel array portion. The pixel array portion has
rows of scanning lines, columns of signal lines, pixels arranged in rows
and columns at intersections of the scanning lines and signal lines, and
power lines arranged in a corresponding manner to the columns of the
pixels. The driver portion has a main scanner for supplying a sequential
control signal to the scanning lines in horizontal periods to scan the
rows of pixels by a line sequential scanning method, a power-supply
scanner for supplying a power-supply voltage switched between a first
potential and a second potential to the power lines in step with the line
sequential scanning, and a signal selector for supplying a selector
output signal to the columns of signal lines in step of the line
sequential scanning. The selector output signal is switched between a
signal potential becoming a video signal within each horizontal period
and a reference potential.

[0010] Each of the pixels includes light-emitting devices, a sampling
transistor, a driving transistor, and a retaining capacitor. The gate of
the sampling transistor is connected with the corresponding one of the
scanning lines. One of the source and drain is connected with the
corresponding one of the signal lines, while the other is connected with
the gate of the driving transistor. One of the source and drain of the
driving transistor is connected with the light-emitting devices, whereas
the other is connected with the power line. The retaining capacitor is
connected between the source and gate of the driving transistor.

[0011] In this display device, the sampling transistor is brought into
conduction according to the control signal supplied from the scanning
line, samples the signal potential supplied from the signal line, and
retains the potential into the retaining capacitor. The driving
transistor receives an electrical current from the power line at the
first potential and supplies a driving current to the light-emitting
devices according to the retained signal potential. The main scanner
outputs a control signal to drive the sampling transistor into conduction
during a first period in which the power line is at the first potential
and, at the same time, the signal line is at the reference potential.
Consequently, a voltage corresponding to a threshold voltage for the
driving transistor is retained in the retaining capacitor. That is, an
operation for correcting the threshold voltage is performed. The main
scanner repeatedly performs the operation for correction of the threshold
voltage in plural horizontal periods preceding the sampling of the signal
potential. This assures that the voltage corresponding to the threshold
voltage for the driving transistor is retained in the retaining
capacitor.

[0012] Preferably, the main scanner outputs the control signal to drive
the sampling transistor into conduction prior to the operation for
correction of the threshold voltage in a time period in which the power
line is at the second potential and, at the same time, the signal line is
at the reference potential. Consequently, the gate of the driving
transistor is set to the reference potential. Also, the source is set to
the second potential. The main scanner outputs a second control signal
shorter in pulse width than the first period to the scanning line to
bring the sampling transistor into conduction when the signal line is at
the signal potential. In consequence, the signal potential is corrected
for the mobility of the driving transistor for holding the signal
potential into the retaining capacitor. At the instant when the signal
potential is retained into the retaining capacitor, the main scanner
brings the sampling transistor out of conduction. The gate of the driving
transistor is electrically disconnected from the signal line. As a
result, the gate potential is made to respond to a variation of the
source potential of the driving transistor, thus maintaining constant the
voltage between the gate and source.

[0013] One embodiment of the present invention provides an active matrix
display device using light-emitting devices, such as organic
electroluminescent devices (OEDs), at pixels. Each pixel has at least a
function of correcting the threshold voltage for the driving transistor.
Preferably, the pixel has the function of correcting the mobility of the
driving transistor and the function of correcting for timewise variations
in the characteristics of the OEDs (bootstrap operation). As a result, a
high image quality can be obtained. To incorporate these corrective
functions, the power-supply voltage supplied to each pixel is used as a
switching pulse. This eliminates switching transistors, which would
normally be used to correct the threshold voltage, and scanning lines,
which control the gate of the switching transistors. As a result, the
number of elements constituting the pixel circuit and the number of lines
can be reduced greatly. Hence, the pixel area can be reduced.
Consequently, a higher resolution of the display can be accomplished. In
the related-art pixel circuit having such corrective functions, there are
many elements, and so the layout area is large. Consequently, the
related-art pixel circuit is unsuited for a higher resolution of display
devices. In one embodiment of the present invention, the number of the
constituent elements and the number of lines are reduced by switching the
power-supply voltage. The pixel layout area can be reduced. Thus, a
high-quality, high-definition flat display can be offered.

[0014] In one embodiment of the present invention, the operation for
correcting the threshold voltage is repeatedly performed in plural
horizontal periods preceding sampling of the signal potential. This
assures that a voltage corresponding to the threshold voltage for the
driving transistor is retained in the retaining capacitor. In one
embodiment of the invention, a correction of the threshold voltage for
the driving transistor is carried out by plural discrete operations and
so the total time to correct the threshold voltage can be secured
sufficiently. The voltage corresponding to the threshold voltage for the
driving transistor can be reliably retained in the retaining capacitor
previously. The voltage which is retained in the retaining capacitor and
which corresponds to the threshold voltage is added to the signal
potential similarly sampled and retained into the retaining capacitor.
This is added to the gate of the driving transistor. The voltage which is
added to the sampled signal potential and which corresponds to the
threshold voltage just cancels the threshold voltage for the driving
transistor. Therefore, a driving current corresponding to the signal
potential can be supplied to the light-emitting devices without being
affected by the variations. For this purpose, it is important that the
voltage corresponding to the threshold voltage be retained in the
retaining capacitor reliably. In one embodiment of the present invention,
writing of the voltage corresponding to the threshold voltage is carried
out by plural discrete repetitive operations. In this way, a time for the
writing is secured sufficiently. Because of this configuration, a
brightness nonuniformity, especially at low gray levels, can be
suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a circuit diagram of a general pixel structure.

[0016] FIG. 2 is a timing chart illustrating the operation of the pixel
circuit shown in FIG. 1.

[0017] FIG. 3A is a block diagram showing the whole structure of a display
device according to one embodiment of the present invention.

[0018] FIG. 3B is a circuit diagram of one example of a display device
according to one embodiment of the invention.

[0019] FIG. 4A is a timing chart illustrating the operation of the example
shown in FIG. 3B.

[0020] FIG. 4B is a circuit diagram illustrating the operation.

[0021] FIG. 4C is a circuit diagram illustrating the operation.

[0022] FIG. 4D is a circuit diagram illustrating the operation.

[0023] FIG. 4E is a circuit diagram illustrating the operation.

[0024] FIG. 4F is a circuit diagram illustrating the operation.

[0025] FIG. 4G is a circuit diagram illustrating the operation.

[0026] FIG. 4H is a circuit diagram illustrating the operation.

[0027] FIG. 4I is a circuit diagram illustrating the operation.

[0028] FIG. 4J is a circuit diagram illustrating the operation.

[0029] FIG. 4K is a circuit diagram illustrating the operation.

[0030] FIG. 4L is a circuit diagram illustrating the operation.

[0031] FIG. 5 shows graphs illustrating the operation of a display device
according to an embodiment of the invention.

[0032] FIG. 6A is a timing chart showing a reference example of a method
of driving a display device.

[0033] FIG. 6B is a circuit diagram illustrating the operation of the
reference example.

[0034] FIG. 6C is a circuit diagram illustrating the operation of the
reference example.

[0035] FIG. 6D is a circuit diagram illustrating the operation of the
reference example.

[0036] FIG. 6E is a circuit diagram illustrating the operation of the
reference example.

[0037] FIG. 6F is a circuit diagram illustrating the operation of the
reference example.

[0038] FIG. 6G is a circuit diagram illustrating the operation of the
reference example.

[0039] FIG. 6H is a circuit diagram illustrating the operation of the
reference example.

[0040] FIG. 6I is a circuit diagram illustrating the operation of the
reference example.

[0041] FIG. 7 is a graph showing the current-voltage characteristics of a
driving transistor.

[0042] FIG. 8A is a graph showing the current-voltage characteristics of
the driving transistor.

[0043] FIG. 8B is a circuit diagram illustrating the operation of a
display device according to an embodiment of the present invention.

[0044] FIG. 8C is a graph of the current-voltage characteristics
illustrating the operation.

[0045] FIG. 9A is a graph showing the current-voltage characteristics of a
light-emitting device.

[0046] FIG. 9B is a waveform diagram illustrating the bootstrap operation
of a driving transistor.

[0047] FIG. 9C is a circuit diagram illustrating the operation of a
display device according to an embodiment of the invention.

[0048] FIG. 10 is a circuit diagram showing another example of a display
device according to an embodiment of the invention.

[0049] FIG. 11 is a cross-sectional view showing the structure of a
display device according to an embodiment of the invention.

[0050] FIG. 12 is a plan view of a modular structure of a display device
according to an embodiment of the invention.

[0051] FIG. 13 is a perspective view of a television set equipped with a
display device according to an embodiment of the invention.

[0052] FIG. 14 is a perspective view of a digital still camera equipped
with a display device according to an embodiment of the invention.

[0053] FIG. 15 is a perspective view of a notebook personal computer
equipped with a display device according to an embodiment of the
invention.

[0054] FIG. 16 is a schematic representation of a mobile terminal unit
equipped with a display device according to an embodiment of the
invention.

[0055] FIG. 17 is a perspective view of a video camera equipped with a
display device according to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Embodiments of the present invention are hereinafter described in
detail with reference to the drawings. To facilitate understanding the
present invention and make clear the background of the invention, a
general structure of a display device is briefly described by referring
to FIG. 1. FIG. 1 is a schematic circuit diagram of one pixel of a
general display device. As shown, in this pixel circuit, a transistor 1A
for sampling is disposed at the intersection of a scanning line 1E and a
signal line 1F which are orthogonal to each other. The transistor 1A is
of the N type. The gate of the transistor is connected with the scanning
line 1E, while the drain is connected with the signal line 1F. One
electrode of a retaining capacitor 1C and the gate of a driving
transistor 1B are connected with the source of the sampling transistor
1A. The driving transistor 1B is of the N type. A power-supply line 1G is
connected with the drain of the driving transistor 1B. The anode of a
light-emitting device 1D is connected with the source of the transistor
1B. The other electrode of the capacitor 1C and the cathode of the
light-emitting device 1D are connected with a grounding line 1H.

[0057] FIG. 2 is a timing chart illustrating the operation of the pixel
circuit shown in FIG. 1. The timing chart illustrates the operation for
causing the light-emitting device 1D made of an organic
electroluminescent device to emit light by sampling the potential of the
video signal supplied from the signal line 1F (potential at the video
signal line). The potential at the scanning line 1E (scanning line
potential) goes to a high level. As a result, the sampling transistor 1A
is turned on. The potential at the video signal line is stored in the
retaining capacitor 1C. Consequently, the gate potential Vg of the
driving transistor 1B begins to rise and starts to supply a drain current
. The anode potential of the light-emitting device 1D rises, starting the
emission of light. Then, if the scanning line potential goes to a low
level, the potential at the video signal line is retained in the
retaining capacitor 1C. The gate potential of the driving transistor 1B
is kept constant. The emission brightness is kept constant up to the next
frame.

[0058] However, the individual pixels vary in characteristics, such as
threshold voltage and mobility, due among respective pixels to variations
in the process for fabricating the driving transistor 1B. Because of the
variations in the characteristics, if the same gate potential is applied
to the driving transistor 1B, the drain current (driving current) varies
among the pixels. This produces variations in the output brightness.
Furthermore, because of timewise variations in the characteristics of the
light-emitting device 1D made of an organic electroluminescent device or
the like, the anode potential of the light-emitting device 1D varies.
This causes variations in the gate-source voltage of the driving
transistor 1B, resulting in variations in the drain current (driving
current). Variations in the driving current produced by these various
causes appear as variations in output brightness among individual pixels.
Consequently, the image quality is deteriorated.

[0059] FIG. 3A is a block diagram of the whole structure of a display
device according to an embodiment of the present invention. As shown, the
present display device, generally indicated by reference numeral 100,
includes a pixel array portion 102 and driver circuitry (103, 104, 105)
for driving the pixel array portion. The pixel array portion 102 has rows
of scanning lines WSL101-WSL10m, rows of signal lines DTL101-DTL10n, a
matrix of pixels (PXLC) 101 arranged at the intersections of the scanning
lines and signal lines, and power lines DSL101-DSL10m arranged in a
corresponding manner to the rows of pixels 101. The driver circuitry
(103, 104, 105) has a main scanner (write scanner WSCN) 104 for supplying
a sequential control signal to each of the scanning lines WSL101-WSL10m
during each horizontal period (1H) to scan the rows of pixels 101 in a
line sequential manner, a power-supply scanner (DSCN) 105 for supplying a
power-supply voltage to each of the power lines DSL101-DSL10m in step
with the line sequential scanning, and a signal selector (horizontal
selector HSEL) 103 for supplying a selector output signal to the columns
of signal lines DTL101-DTL10m in step with the line sequential scanning
during each horizontal period 1H. The power-supply voltage is switched
between first and second potentials. The selector output signal is
switched between a signal potential becoming a video signal and a
reference potential.

[0060] FIG. 3B is a circuit diagram showing the details of the structure
of the pixels 101 contained in the display device 100 shown in FIG. 3A
and the connective relationship. As shown, one pixel 101 includes a
light-emitting device 3D typified by an organic electroluminescent
device, a transistor 3A for sampling, a driving transistor 3B, and a
retaining capacitor 3C. The gate of the sampling transistor 3A is
connected with the corresponding scanning line WSL101. One of the source
and drain is connected with the corresponding signal line DTL101. The
other is connected with the gate g of the driving transistor 3B. One of
the source s and drain d of the driving transistor 3B is connected with
the light-emitting device 3D, while the other is connected with the
corresponding power line DSL101. In the present embodiment, the drain d
of the driving transistor 3B is connected with the power line DSL101,
while the source s is connected with the anode of the light-emitting
device 3D. The cathode of the light-emitting device 3D is connected with
a grounding line 3H. The grounding line 3H is connected with all the
pixels 101 in common. The retaining capacitor 3C is connected between the
source s and gate g of the driving transistor 3B.

[0061] In this structure, the sampling transistor 3A conducts in response
to the control signal supplied from the scanning line WSL101, samples the
signal potential supplied from the signal line DTL101, and retains the
sampled potential into the retaining capacitor 3C. The driving transistor
3B receives an electrical current from the power line DSL101 at the first
potential and supplies a driving current to the light-emitting device 3D
in response to the signal potential retained in the retaining capacitor
3C. The main scanner 104 outputs a control signal to the sampling
transistor 3A to bring it into conduction during a period in which the
power line DSL101 is at the first potential and, at the same time, the
signal line DTL101 is at the reference potential to perform an operation
for correcting the threshold voltage for retaining the voltage
corresponding to the threshold voltage Vth for the driving transistor 3B
into the retaining capacitor 3C.

[0062] As one embodiment of the present invention, the main scanner 104
repeatedly performs an operation for correcting the threshold voltage in
plural horizontal periods preceding sampling of the signal potential to
ensure that a voltage corresponding to the threshold voltage Vth for the
driving transistor 3B is retained in the retaining capacitor 3C. In this
way, in the embodiment of the invention, a sufficiently long writing
period is secured by performing plural operations for correcting the
threshold voltage. Consequently, the voltage corresponding to the
threshold voltage for the driving transistor can be reliably and
previously retained in the retaining capacitor 3C. The retained voltage
corresponding to the threshold voltage is used to cancel the threshold
voltage for the driving transistor. Accordingly, if the threshold voltage
for the driving transistor varies among the individual pixels, the
variations among the pixels are completely canceled out. As a result, the
uniformity of the image is enhanced. Especially, the brightness
nonuniformity that tends to appear at low gray levels represented by the
signal potential can be prevented.

[0063] Preferably, the main scanner 104 outputs a control signal to bring
the sampling transistor 3A into conduction during a period in which the
power line DSL101 is at the second potential and, at the same time, the
signal line DTL101 is at the reference potential prior to the operation
for correcting the threshold voltage. Consequently, the gate g of the
driving transistor 3B is set to the reference potential. The source s is
set to the second potential. The operations for resetting the gate
potential and source potential ensure that an operation for correcting
the threshold voltage, as described later, is performed.

[0064] The pixel 101 shown in FIG. 3B has a mobility-correcting function
in addition to the aforementioned function of correcting the threshold
voltage. That is, in order to bring the sampling transistor 3A into
conduction during the period in which the signal line DTL101 is at the
signal potential, the main scanner 104 outputs a control signal having a
pulse width shorter than the above-described period to the scanning line
WSL101. Therefore, when the signal potential is retained into the
retaining capacitor 3C, the signal potential is simultaneously corrected
for the mobility μ of the driving transistor 3B.

[0065] Furthermore, the pixel circuit 101 shown in FIG. 3B has a bootstrap
function. That is, when the signal potential is retained into the
retaining capacitor 3C, the main scanner (WSCN) 104 ceases to apply the
control signal to the scanning line WSL101, bringing the sampling
transistor 3A out of conduction. The gate g of the driving transistor 3B
is electrically disconnected from the signal line DTL101. Consequently,
the gate potential (Vg) responds to a variation of the source potential
(Vs) of the driving transistor 3B. As a result, the voltage Vgs between
the gate g and source s can be maintained constantly.

[0066] FIG. 4A is a timing chart illustrating the operation of the pixel
101 shown in FIG. 3B. The time axis is taken as a common axis. Variations
in the potential at the scanning line WSL101, variations in the potential
at the power line DSL101, and variations of the potential at the signal
line DTL101 are shown. Variations in the gate potential Vg of the driving
transistor 3B and variations in the source potential Vs are shown beside
those variations.

[0067] In the timing chart, the time is conveniently partitioned into
periods (B)-(L) in step with the progress of the operation of the pixel
101. In the emission period (B), the light-emitting device 3D is emitting
light. Then, the process enters a new field of a line sequential scanning
operation. In the first period (C), the power line DSL101 is switched
from a high potential (Vcc_H) to a low potential (Vcc_L). Then, in a
preparatory period (D), the gate potential Vg of the driving transistor
3B is reset to the reference potential Vo. Furthermore, the source
potential Vs is reset to the low potential Vcc_L of the power line
DTL101. Subsequently, the first operation for correcting the threshold
voltage is performed in the first threshold correction period (E).
Because only one operation is performed, a sufficiently long time period
is not obtained. Consequently, the voltage written into the retaining
capacitor 3C is Vx1, which does not reach the threshold voltage Vth for
the driving transistor 3B.

[0068] An elapsing period (F) follows. Then, the second threshold
voltage-correcting period (G) occurs in the next horizontal period (1H).
At this time, the second operation for correcting the threshold voltage
is performed. The voltage Vx2 written into the retaining capacitor 3C
approaches Vth. Another elapsing period (H) follows. Then, the third
threshold voltage-correcting period (I) occurs in the next one horizontal
period (1H). The third operation for correcting the threshold voltage is
performed. Consequently, the voltage written into the retaining capacitor
3C reaches the threshold voltage Vth for the driving transistor 3B.

[0069] In the latter half of the final one horizontal period, the
potential at the video signal line DTL101 rises from the reference
voltage Vo to the signal potential Vin. After a lapse of a period of J,
the signal potential Vin of the video signal is written into the
retaining capacitor 3C such that the potential Vin is added to Vth during
a sampling period/mobility correction period (K). A voltage ΔV for
correction of the mobility is subtracted from the voltage retained in the
retaining capacitor 3C. Then, an emission period (L) follows. The
light-emitting device emits light at a brightness corresponding to the
signal voltage Vin. At this time, since the signal voltage Vin is
adjusted by the voltage corresponding to the threshold voltage Vth and
the voltage ΔV for correction of the mobility, the brightness of
the emission from the light-emitting device 3D is affected neither by
variations in the threshold voltage Vth for the driving transistor 3B nor
by variations in the mobility μ. At the beginning of the emission
period (L), a bootstrap operation is performed. The gate potential Vg and
source potential Vs of the driving transistor 3B are increased while
maintaining a constant gate/source voltage Vgs=Vin+Vth-ΔV of the
driving transistor 3B.

[0070] In the embodiment shown in FIG. 4A, the operation for correcting
the threshold voltage is repeated three times. The three operations for
the corrections are carried out in the periods E, G, and I, respectively.
These periods E, G, and I belong to the former halves of the horizontal
periods (1H). In these periods, the signal line DTL101 is at the
reference potential Vo. In the periods, the potential at the scanning
line WSL101 is switched to a high level to turn on the sampling
transistor 3A. As a result, the gate potential Vg of the driving
transistor 3B becomes equal to the reference potential Vo. During this
period, an operation for correcting the threshold voltage of the driving
transistor 3B is performed. In the latter halves of the horizontal
periods (1H), the signal potential is sampled for other rows of pixels.
Accordingly, in the periods (F) and (H), the potential at the scanning
line WSL101 is switched to a low level, turning off the sampling
transistor 3A. These operations are repeated. The gate-source voltage Vgs
of the driving transistor 3B soon reaches the threshold voltage Vth for
the driving transistor 3B. The number of repetitions of the operation for
correcting the threshold voltage is optimally set according to the pixel
circuit configuration. Consequently, the operations for correcting the
threshold voltage are performed reliably. Hence, good image quality can
be obtained at all the gray levels from the lowest level (i.e. , the
black level) to the highest level (i.e. , the white level).

[0071] Referring still to FIGS. 4B-4L, the operation of the pixel 101
shown in FIG. 3B is described in detail. The figure numbers given to
FIGS. 4B-4L correspond to periods (B)-(L), respectively, in the timing
chart shown in FIG. 4A. To facilitate understanding, the capacitive
component of the light-emitting device 3D is shown as a capacitive
element 3I for the sake of convenience of illustration in FIGS. 4B-4L.
First, as shown in FIG. 4B, in the emission period (B), the power supply
line DSL101 is at a high potential of Vcc_H (first potential). The
driving transistor 3B is supplying a driving current Ids to the
light-emitting device 3D. As shown, the driving current Ids passes into
the light-emitting device 3D from the power supply line DSL101 at the
high potential of Vcc_H via the driving transistor 3B, and flows into a
common grounding line 3H.

[0072] The period (C) follows. As shown in FIG. 4C, the power supply line
DSL101 is switched from a high potential Vcc_H to a low potential Vcc_L.
Thus, the power supply line DSL101 is discharged until the low potential
Vcc_L is reached. Furthermore, the source potential Vs of the driving
transistor 3B goes to a potential close to Vcc_L. Where the line
capacitance of the power supply line DSL101 is large, it is better to
switch the power supply line DSL101 from the high potential Vcc_H to the
low potential Vcc_L at a relatively early timing. The effects of the line
capacitance and other pixel parasitic capacitors can be eliminated by
making the period (C) sufficiently long.

[0073] Then, the period (D) follows. As shown in FIG. 4D, the sampling
transistor 3A is brought into conduction by switching the scanning line
WSL101 from a low level to a high level. At this time, the video signal
line DTL101 is at the reference potential Vo. Therefore, the gate
potential Vg of the driving transistor 3B is made equal to the reference
potential Vo at the video signal line DTL101 through the conducting
sampling transistor 3A. The source potential Vs of the driving transistor
3B is quickly fixed at the low potential Vcc_L. As a result, the source
potential Vs of the driving transistor 3B is reset to the potential Vcc_L
that is sufficiently lower than the reference potential Vo at the video
signal line DTL. In particular, the low potential Vcc_L (second
potential) at the power supply line DSL101 is so set that the gate-source
voltage Vgs (difference between the gate potential Vg and source
potential Vs) of the driving transistor 3B becomes greater than the
threshold voltage Vth for the driving transistor 3B.

[0074] Then, the first period (E) for correction of the threshold value
follows. As shown in FIG. 4E, the potential at the power supply line
DSL101 goes from the low potential Vcc_L to the high potential Vcc_H. The
source potential Vs of the driving transistor 3B begins to rise. This
period (E) ends when the source potential Vs makes a transition from
Vcc_L to Vx1. Therefore, Vx1 is written into the retaining capacitor 3C
in the first period (E) for correction of the threshold value.

[0075] Subsequently, in the latter half (F) of this horizontal period
(1H), the potential at the video signal line varies to the signal
potential Vin while the potential at the scanning line WSL101 goes to a
low level as shown in FIG. 4F. In this period (F), the signal potential
Vin is sampled for the other rows of pixels. It is necessary that the
sampling transistor 3A of the pixels be turned off.

[0076] The former half of the next 1 horizontal period (1H) is another
threshold value correction period (G). As shown in FIG. 4G, a second
operation for correction of the threshold value is performed. In the same
way as in the first operation, the video signal line DTL101 becomes the
reference potential Vo, and a scanning line WSL101 goes to a high level.
The sampling transistor 3A is turned on. Because of these operations,
writing of the potential into the retaining capacitor 3C is made to
progress. The potential reaches Vx2.

[0077] In the latter half (H) of this horizontal period (1H), in order to
sample the signal potential for the other rows of pixels, the scanning
line WSL101 of the rows is made to go low. The sampling transistor 3A is
turned off.

[0078] In the third period (I) for correction of the threshold value, the
scanning line WSL101 is again switched to a high level, as shown in FIG.
4I, to turn on the sampling transistor 3A. The source potential Vs of the
driving transistor 33 starts to rise. Just when the gate-source voltage
Vgs of the driving transistor 3B reaches the threshold voltage Vth, the
current is cut off. In this way, a voltage corresponding to the threshold
voltage Vth for the driving transistor 3B is written into the retaining
capacitor 3C. In all of the three periods (E), (G), and (I) for
correction of the threshold value, the potential at the common grounding
line 3H is so set that the light-emitting device 3D is cut off such that
all the driving current flows through the retaining capacitor 3C but does
not flow through the light-emitting device 3D.

[0079] In the following period (J), the potential at the video signal line
DTL101 goes to the sampling potential (signal potential) Vin from the
reference potential Vo as shown in FIG. 4J. Thus, preparations for the
next sampling operation and operation for correction of the mobility are
completed.

[0080] When the process enters the sampling period/mobility correction
period (K), the potential at the scanning line WSL101 goes to the higher
potential side, as shown in FIG. 4K. The sampling transistor 3A is turned
on. Accordingly, the gate potential Vg of the driving transistor 3B
becomes equal to the signal potential Vin. Since the light-emitting
device 3D is in the cutoff state (high impedance state) at first, the
drain-source current Ids of the driving transistor 3B flows into the
light-emitting device capacitor 31. The capacitor starts to be charged.
Therefore, the source potential Vs of the driving transistor 3B starts to
rise. The gate-source voltage Vgs of the driving transistor 3B soon
reaches (Vin+Vth-ΔV) . In this way, sampling of the signal
potential Vin and adjustment of the amount of correction ΔV are
performed at the same time. As the potential Vin is increased, the
current Ids is increased, and the absolute value of ΔV also is
increased. Accordingly, a mobility correction is made according to the
level of the emission brightness. Where it is assumed that the potential
Vin is constant, the absolute value of ΔV is increased with
increasing the mobility μ of the driving transistor 3B. In other
words, as the mobility μ is increased, the amount of negative feedback
ΔV is increased. Consequently, variations in mobility μ among
individual pixels can be eliminated.

[0081] Finally, the process enters the emission period (L). As shown in
FIG. 4L, the scanning line WSL101 makes a transition to the lower
potential side, turning off the sampling transistor 3A. Consequently, the
gate g of the driving transistor 3B is disconnected from the signal line
DTL101. At the same time, the drain current Ids starts to flow through
the light-emitting device 3D. Thus, the anode potential at the
light-emitting device 3D rises by an amount of Vel according to the
driving current Ids. The rise of the anode potential of the
light-emitting device 3D is none other than an increase of the source
potential Vs of the driving transistor 3B. When the source potential Vs
of the driving transistor 3B rises, the gate potential Vg of the driving
transistor 3B is increased responsively by the bootstrap operation of the
retaining capacitor 3C. The amount of increase Vel of the gate potential
Vg becomes equal to the amount of increase Vel of the source potential
Vs. Therefore, during the emission period, the gate-source voltage Vgs of
the driving transistor 3B is kept at a constant value of
(Vin+Vth-ΔV).

[0082] As is obvious from the description provided so far, in a display
device according to an embodiment of the present invention, each pixel
has a threshold voltage-correcting function and a mobility-correcting
function. FIG. 5 shows graphs representing the current-voltage
characteristics of the driving transistor included in each pixel having
such corrective functions. In each graph, the signal potential Vin is
plotted on the horizontal axis, while the driving current Ids is plotted
on the vertical axis. The Vin/Ids characteristics of different pixels A
and B are graphed. At the pixel A, the threshold voltage Vth is
relatively low and the mobility μ is relatively large. Conversely, at
the pixel. B, the threshold voltage Vth is relatively high but the
mobility μ is relatively small.

[0083] Graph (1) shows a case where the correction of the threshold value
and the correction of the mobility are not done. At this time, at the
pixels A and B, neither the threshold voltage Vth nor the mobility μ
is corrected. Therefore, the pixels are greatly different in Vin/Ids
characteristics depending on variations in Vth and μ. Accordingly, if
the same signal potential Vin is given, the driving current Ids becomes
different. That is, the emission brightness becomes different. A good
uniformity across the screen is not obtained.

[0084] Graph (2) shows a case where the threshold value is corrected but
the mobility is not corrected. At this time, the difference in Vth
between the pixels A and B is canceled out. However, the difference in
the mobility μ appears intact. Therefore, in a region where Vin is
high (i.e. , where the brightness is high) , the difference in the
mobility μ appears conspicuously. Different levels of brightness
appear even at the same gray level. More specifically, at the same gray
level (at the same Vin), the pixel A having the larger mobility μ
produces a higher level of brightness (higher level of driving current
Ids). The pixel B having the smaller mobility μ produces a lower level
of brightness.

[0085] Graph (3) shows a case where both the correction of the threshold
value and the correction of the mobility have been carried out. This case
corresponds to an embodiment of the present invention. Differences caused
by variations in the threshold voltage Vth and the mobility μ have
been completely corrected. As a result, the pixels A and B are coincident
in Vin/Ids characteristics. Accordingly, at all the gray levels (Vin),
both pixels are identical in level of brightness (Ids). The uniformity
across the screen has been improved conspicuously.

[0086] Graph (4) shows a reference example where the mobility has been
corrected but the threshold voltage has been corrected insufficiently. In
other words, the operation for correcting the threshold voltage is
performed only once rather than repeated plural times. At this time, the
difference in the threshold voltage Vth is not removed, and so the pixels
A and B differ in brightness (driving current Ids) at low gray levels.
Consequently, where the threshold voltage is corrected insufficiently,
the brightness is not uniform at low gray levels, impairing the image
quality.

[0087] FIG. 6A is a timing chart showing a reference example of the method
of driving the display device shown in FIG. 3B. The identical notation is
used in both timing charts of FIGS. 3B and 4A to facilitate
understanding. The timing chart of FIG. 4A illustrates a method of
driving the display device according to one embodiment of the present
invention. The difference with the method of driving the display device
shown in FIG. 4A in accordance with one embodiment of the present
invention is that only one operation for correcting the threshold voltage
is performed in this reference example.

[0088] Operations performed in the periods (B)-(I) in the timing chart
shown in FIG. 6A are described briefly by referring still to FIGS. 6B-6I.
First, as shown in FIG. 6B, in the emission period (B), the power supply
line DSL101 is at the high potential Vcc_H (first potential). The driving
transistor 3B is supplying the driving current Ids to the light-emitting
device 3D. As shown, the driving current Ids passes from the power supply
line DSL101 at the high potential Vcc_H into the light-emitting device 3D
via the driving transistor 3B and flows into the common grounding line
3H.

[0089] Then, the process enters the period (C). As shown in FIG. 6C, the
power supply line DSL101 is switched from the high potential Vcc_H to the
low potential Vcc_L. Thus, the power supply line DSL101 is discharged to
the potential Vcc_L. Furthermore, the source potential Vs of the driving
transistor 3B goes to a potential close to Vcc_L. Where the line
capacitance of the power supply line DSL101 is large, it is better to
switch the power supply line DSL101 from the high potential Vcc_H to the
low potential Vcc_L at a relatively early timing. The effects of the line
capacitor and other pixel parasitic capacitors can be eliminated by
making the period (C) sufficiently long.

[0090] Then, the process goes to the period (D). The sampling transistor
3A is brought into conduction by switching the scanning line WSL101 from
a low level to a high level, as shown in FIG. 6D. At this time, the video
signal line DTL101 is at the reference potential Vo. Therefore, the gate
potential Vg of the driving transistor 3B is made equal to the reference
potential Vo of the video signal line DTL101 through the conducting
sampling transistor 3A. At the same time, the source potential Vs of the
driving transistor 3B is quickly fixed at the low potential Vcc_L.
Because of the operations described so far, the source potential Vs of
the driving transistor 3B is reset to the initial potential, i.e., the
potential Vcc_L that is sufficiently lower than the reference potential
Vo at the video signal line DTL. In particular, the low potential Vcc_L
(second potential) at the power supply line DSL101 is so set that the
gate-source voltage Vgs (difference between the gate potential Vg and
source potential Vs) of the driving transistor 3B becomes greater than
the threshold voltage Vth for the driving transistor 3B.

[0091] Then, the process goes to the threshold value correction period
(E). As shown in FIG. 6E, the power supply line DSL101 makes a transition
from the low potential Vcc_L to the high potential Vcc_H. The source
potential Vs of the driving transistor 3B begins to rise. The gate-source
voltage Vgs of the driving transistor 3B soon reaches the threshold
voltage Vth. At this time, the current is cut off. In this way, a voltage
corresponding to the threshold voltage Vth for the driving transistor 3B
is written into the retaining capacitor 3C. This is the operation for
correcting the threshold voltage. The potential at the common grounding
line 3H is so set that the light-emitting device 3D is cut off such that
all the current flows through the retaining capacitor 3C but does not
flow through the light-emitting device 3D. In practice, however, the
single operation for correcting the threshold voltage may not provide a
sufficient time. That is, the single operation may not make it possible
to write a voltage corresponding to the threshold voltage Vth for the
driving transistor 3B completely into the retaining capacitor 3C.

[0092] The process goes to the period (F). As shown in FIG. 6F, the
potential at the scanning line WSL101 makes a transition to the lower
potential side. The sampling transistor 3A is once turned off. At this
time, the gate g of the driving transistor 3B is floated. Because the
gate-source voltage Vgs is equal to the threshold voltage Vth for the
driving transistor 3B, the transistor is cut off. The drain current Ids
does not flow.

[0093] Then, the process goes to the period (G). As shown in FIG. 6G, the
potential at the video signal line DTL101 makes a transition from the
reference potential Vo to the sampling potential (signal potential) Vin.
In this way, preparations for the next sampling operation and for the
operation for correction of the mobility are completed.

[0094] When the process enters the sampling period/mobility correction
period (H), the potential at the scanning line WSL101 makes a transition
to the higher potential side as shown in FIG. 6H. The sampling transistor
3A is turned on. Accordingly, the gate potential Vg of the driving
transistor 3b becomes equal to the signal potential Vin. Since the
light-emitting device 3D is in the cutoff state (high impedance state) at
first, the drain-source current Ids of the driving transistor 3B flows
into the light-emitting capacitor 3I. The capacitor starts to be charged.
Therefore, the source potential Vs of the driving transistor 3B starts to
rise. The gate-source voltage Vgs of the driving transistor 3B soon
reaches (Vin+Vth-ΔV). In this way, sampling of the signal potential
Vin and adjusting the amount of correction ΔV are performed at the
same time. As Vin is increased, Ids is increased, and the absolute value
of ΔV also is increased. Accordingly, a mobility correction is made
according to the level of the emission brightness. Where it is assumed
that Vin is constant, the absolute value of ΔV is increased with
increasing the mobility μ of the driving transistor 3B. In other
words, as the mobility μ is increased, the amount of negative feedback
ΔV is increased. Consequently, variations in mobility μ among
the individual pixels can be removed.

[0095] Finally, the process goes to the emission period (I). As shown in
FIG. 61, the scanning line WSL101 make a transition to the lower
potential side. The sampling transistor 3A is turned off. Consequently,
the gate g of the driving transistor 3B is disconnected from the signal
line DTL101. At the same time, the drain current Ids starts to flow
through the light-emitting device 3D. Consequently, the anode potential
of the light-emitting device 3D rises by an amount Vel in response to the
driving current Ids. The increase in the anode potential of the
light-emitting device 3D is none other than an increase in the source
potential Vs of the driving transistor 3B. When the source potential Vs
of the driving transistor 3B rises, the gate potential Vg of the driving
transistor 3B is increased responsively by the bootstrap operation of the
retaining capacitor 3C. The amount of increase Vel of the gate potential
Vg becomes equal to the amount of increase Vel of the source potential
Vs. Therefore, during the emission period, the gate-source voltage Vgs of
the driving transistor 3B is kept at a constant value of
(Vin+Vth-ΔV).

[0096] Finally, for the sake of references, the operation for correcting
the threshold voltage, the operation for correcting the mobility, and the
bootstrap operation, all performed in a display device according to an
embodiment of the present invention, are described in detail.

[0097] FIG. 7 is a graph showing the current-voltage characteristics of
the driving transistor. Especially, when the driving transistor is
operating in the saturation region, the drain-source current Ids is given
by

Ids=(1/2)μ(W/L)Cox(Vgs-Vth)2

where μ indicates the mobility, W indicates the gate width, L
indicates the gate length, and Cox indicates the gate oxide film
capacitance per unit area. As is obvious from this equation indicating
the transistor characteristics, when the threshold voltage Vth varies,
the drain-source current Ids varies even if the voltage Vgs is constant.
At each pixel according to an embodiment of the present invention, the
gate-source voltage Vgs during emission is given by (Vin+Vth-ΔV),
as described previously. When this is substituted into the above equation
for the transistor characteristics, the drain-source current Ids is given
by

Ids=(1/2)μ(W/L)Cox(Vin-ΔV)2

Therefore, the current Ids does not depend on the threshold voltage Vth.
As a result, if the threshold voltage Vth varies due to the manufacturing
process, the drain-source current Ids does not vary. Furthermore, the
emission brightness of the organic electroluminescent device does not
vary.

[0098] Where no countermeasures are taken, the driving current
corresponding to the Vgs when the threshold voltage is Vth is ids, as
shown in FIG. 7. However, when the threshold voltage is Vth', the driving
current corresponding to the same gate voltage Vgs assumes a value of
Ids' different from Ids.

[0099] Similarly, FIG. 8A is a graph showing the current-voltage
characteristics of driving transistors. The characteristic curves of two
driving transistors having mobilities of μ and μ', respectively,
are shown. As can be seen from the graph, the drain-source currents of
the two transistors having the different values of mobility μ and
μ', respectively, are Ids and Ids', respectively. That is, the
transistors differ in drain-source current if they have the same value of
Vgs.

[0100] FIG. 8B illustrates the operation of a pixel when the video signal
potential is sampled and when the mobility is corrected. To facilitate
understanding, a parasitic capacitor 3I of a light-emitting device 3D
also is shown. When the video signal potential is sampled, the sampling
transistor 3A is conducting (ON), and so the gate potential Vg of the
driving transistor 3B is the video signal potential Vin. The gate-source
voltage Vgs of the driving transistor 3B is (Vin+Vth). At this time, the
driving transistor 3B is conducting (ON). The light-emitting device 3D is
cut off. Therefore, the drain-source current Ids flows into the
light-emitting device capacitor 3I. If the drain-source current Ids flows
into the light-emitting device capacitor 3I, the capacitor 3I starts to
be electrically charged. The anode potential of the light-emitting device
3D (therefore, the source potential Vs of the driving transistor 3B)
starts to rise. When the source potential Vs of the driving transistor 3B
rises by ΔV, the gate-source voltage Vgs of the driving transistor
3B decreases by ΔV. This is an operation for correcting the
mobility by making use of negative feedback. The amount of decrease
ΔV of the gate-source voltage Vgs is determined by

ΔV=IdsCel/t

where ΔV is a parameter for correcting the mobility, Cel indicates
the value of the capacitance of the light-emitting device capacitor 3I,
and t indicates the period in which the mobility is corrected.

[0101] FIG. 8C is a graph illustrating operating points of the driving
transistor 3B when the mobility is corrected. Where different values of
mobility μ and μ' are produced due to manufacturing process
variations, optimum corrective parameters ΔV and ΔV' are
determined by making the aforementioned mobility correction. The
drain-source currents Ids and Ids' of the driving transistor 3B are
determined. If the mobility correction is not made, and if there are
different values of mobility μ and μ' for the gate-source voltage
Vgs, the drain-source current produces different values of IdsO and IdsO'
accordingly. To cope with this, the values of the drain-source current
are brought to the same level of Ids and Ids' by applying appropriate
corrections ΔV and ΔV' to the mobilities μ and μ',
respectively. As can be seen from the graph of FIG. 8C, a negative
feedback is applied to increase the amount of correction ΔV when
the mobility μ is large and to reduce the amount of correction
ΔV' when the mobility μ' is small.

[0102] FIG. 9A is a graph showing the current-voltage characteristics of
the light-emitting device 3D made of an organic electroluminescent
device. When current Iel flows through the light-emitting device 3D, the
anode-cathode voltage Vel is uniquely determined. During the emission
period, the potential at the scanning line WSL101 makes a transition to
the lower potential side. When the sampling transistor 3A is turned off,
the potential at the anode of the light-emitting device 3D rises by an
amount equal to the anode-cathode voltage Vel determined by the
drain-source current Ids of the driving transistor 3B.

[0103] FIG. 9B is a graph showing variations in the gate potential Vg and
in the source potential Vs of the driving transistor 3B when the anode
potential of the light-emitting device 3D rises. When the amount of
increase of the potential at the anode of the light-emitting device 3D is
Vel, the potential at the source of the driving transistor 3B also rises
by Vel. The potential at the gate of the driving transistor 3B is
increased by Vel by a bootstrap operation of the retaining capacitor 3C.
Therefore, the gate-source voltage, Vgs=Vin+Vth-ΔV, of the driving
transistor 3B retained before the bootstrap operation is maintained
intact after the bootstrap. Furthermore, if the anode potential of the
light-emitting device 3D varies due to its timewise variations, the
gate-source voltage of the driving transistor 3B is kept at a constant
value of (Vin+Vth-ΔV) at all times.

[0104] FIG. 9C is a circuit diagram of the pixel structure shown in FIG.
3B and built according to an embodiment of the invention, the pixel
structure having parasitic capacitors 7A and 7B added thereto. The
parasitic capacitors 7A and 7B are parasitic on the gate g of the driving
transistor 3B. It is assumed that the retaining capacitor has a
capacitance Cs and that the parasitic capacitors 7A and 7B have
capacitances Cw and Cp, respectively. The aforementioned bootstrapping
capability is given by Cs/(Cs+Cw+Cp). It can be said that the
bootstrapping capability is enhanced as the value is brought closer to 1.
That is, the capability in making a correction for timewise degradation
of the light-emitting device 3D is enhanced. In one embodiment of the
present invention, the number of devices connected with the gate g of the
driving transistor 3B is suppressed to a minimum. Cp can be almost
neglected. Accordingly, the bootstrapping capability is given by
Cs/(Cs+Cw). It follows that the capability is infinitely close to 1. This
indicates that the capability in correcting timewise degradation of the
light-emitting device 3D is high.

[0105] FIG. 10 is a schematic circuit diagram of other example of a
display device according to an embodiment of the present invention. To
facilitate understanding, like components are indicated by like reference
numerals in both FIGS. 3B and 10, it being noted that FIG. 3B shows the
previous example. The difference is that in the example shown in FIG. 3B,
a pixel circuit is built using N-channel transistors, while in the
example shown in FIG. 10, a pixel circuit is built using P-channel
transistors. The pixel circuit shown in FIG. 10 can perform the operation
for correction of the threshold voltage, the operation for correction of
the mobility, and the bootstrap operation in exactly the same way as the
pixel circuit shown in FIG. 3B.

[0106] A display device according to an embodiment of the present
invention has a thin-film device structure, as shown in FIG. 11, which
shows a schematic cross-sectional structure of one of the pixels formed
on an insulating substrate. As shown, the pixel includes transistors
having plural TFTs (in the figure, only one TFT is shown), a capacitor
portion such as a retaining capacitor, and a light-emitting portion such
as an organic electroluminescent device. The transistors and the
capacitor portion are fabricated on a substrate by a TFT fabrication
process. The light-emitting portion, such as an organic
electroluminescent device, is laminated on them. A transparent counter
substrate is bonded to the light-emitting portion via an adhesive, thus
forming a flat panel.

[0107] A display device according to an embodiment of the present
invention can assume a flat modular form as shown in FIG. 12. For
example, a pixel array portion is formed on an insulating substrate. In
the pixel array portion, multiple pixels including organic
electroluminescent devices, thin-film transistors, and thin-film
capacitors are arranged in a matrix. An adhesive is disposed around the
pixel array portion (pixel matrix portion). A counter substrate made of
glass is bonded, thus forming a display module. If necessary, color
filters, a protective film, an optical shielding film, and so on may be
formed on the transparent counter substrate. For example, a flexible
printed circuit (FPC) may be mounted to the display module as a connector
for inputting and outputting signals to the pixel array portion from the
outside.

[0108] The display devices described so far and built according to
embodiments of the present invention have the forms of a flat panel.
These can be utilized as display devices which are used in various
electronic devices (such as a digital camera, a notebook personal
computer, a cell phone, and a video camera) in all fields and which
display video signals entered into the electronic devices or video
signals created within the electronic devices as visible images or
pictures. Examples of the electronic devices utilizing such display
devices are shown below.

[0109] FIG. 13 shows a television set to which an embodiment of the
present invention is applied. The set includes an image display screen 11
including a front panel 12 and a filter glass 13. The television set is
fabricated by using a display device according to an embodiment of the
present invention in the image display screen 11.

[0110] FIG. 14 shows a digital camera to which an embodiment of the
present invention is applied. The upper picture is a front elevation. The
lower picture is a rear view. The digital camera includes an imaging
lens, a light-emitting portion 15 for a flash, a display portion 16,
control switches, a menu switch, and a shutter 19. The digital camera is
fabricated by using a display device according to an embodiment of the
present invention in the display portion 16.

[0111] FIG. 15 shows a notebook personal computer to which an embodiment
of the present invention is applied. The body 20 of the computer includes
a keyboard 21 that is manipulated when alphanumerical characters are
entered. The computer further includes a body cover having a display
portion 22 on which an image is displayed. The notebook personal computer
is fabricated by using a display device according to an embodiment of the
present invention in the display portion 22.

[0112] FIG. 16 shows a mobile terminal unit to which an embodiment of the
present invention is applied. The left picture shows the state in which
the cover is opened. The right picture shows the state in which the cover
is closed. The mobile terminal unit includes an upper housing 23, a lower
housing 24, a connector portion 25 (hinge portion in this example), a
display portion 26, a subdisplay portion 27, a picture light 28, and a
camera 29. The mobile terminal unit is fabricated by using display
devices according to an embodiment of the present invention in the
display portion 26 and in the subdisplay portion 27.

[0113] FIG. 17 shows a video camera to which an embodiment of the present
invention is applied. The video camera includes a body 30, a lens 34
mounted on the front side surface to image the subject, a start-stop
switch 35 manipulated during shooting, and a monitor 36. The video camera
is fabricated by using a display device according to an embodiment of the
invention in the monitor 36.

[0114] It should be understood by those skilled in the art that various
modifications, combinations, subcombinations and alterations may occur
depending on design requirements and other factors insofar as they are
within the scope of the appended claims or the equivalents thereof.